This invention relates to laminated films joined by blocking and processes for producing the same.
As the packaging material used for the packaging bags of photographic photosensitive materials, laminated films consisting of a plurality of film layers are used, and the plurality of the film layers are laminated through an adhesive layer or directly by extrusion laminating. The laminated films are produced through many laminating processes which increase manufacturing cost, and tend to curl. Moreover, tear strength is small.
The inventors disclosed a novel laminated film laminated not by adhesive or extrusion laminating but by blocking in a soft state to a certain degree U.S. Pat. No. 4,981,734, EP 0,369,447A). The laminated films laminated by blocking have a great tear strength, Gelbo test strength and impact puncture strength, and curling does not occur. However, the pseudo-adhesion by blocking is unstable, and laminated films were occasionally separated from a cut end at temperatures. The pseudo-adhesion was also occasionally separated partially in the laminating process with other flexible sheets or in the bag-making process, resulting in the occurrence of wrinkling, furrowing or blistering troubles. These troubles became a problem in winter and in strongly air-cooled room.